Tropical Damselfish Successfully Adapt to Higher Temperatures

Some researchers are predicting that ocean temperatures will rise within the next 50-100 years due to global warming (e.g. Hughes et al., 2003) and tropical species are said to have less ability to adapt to these changes than temperate species because they have evolved in a more stable thermal environment.

To test this supposition, the authors of this report turned to the laboratory, where controlled experiments on tropical damselfish Ancanthochromis polyacanthus could be carried out. They reared the offspring from eight wild-caught damselfish for two generations, "in present day (+0.0°C) and predicted future increased water temperatures (+1.5°C and +3.0°C) to test their capacity for metabolic acclimation to ocean warming."

After three months, they assessed the responses in resting metabolic rate (RMR) relative to maximum metabolic rate (MMR) for each individual. This 'metabolic performance' measure was used to characterize changes in the ability of each fish to perform aerobic activities (which would include such functions as behavior, growth and reproduction) at its summer average water temperature (+0.0°C) and above (+1.5°C and +3.0°C).

It was found that second generation offspring had superior metabolic performance at all temperatures when their parents had been reared to maturity at a temperature of +1.5°C or +3.0°C. In addition, one pair of damselfish (i.e. one particular genetic lineage) contributed many more second generation offspring that did well at +3.0°C than did the other wild parents: 75% of all fish that reproduced at +3.0°C were the offspring of wild pair #41. In contrast, wild pair #41 contributed 57% of offspring reproducing at +1.5°C and only 44% of those reproducing at +0.0°C. Thus, in addition to acclimation occurring within two generations, there was also rapid selection of genotypes (and associated phenotypes) that were tolerant of higher temperatures.

In their conclusions, Donelson et al. state: "this study provides evidence that, contrary to some expectations, a tropical marine species has the capacity for acclimation and adaptation to temperature increases over timescales much shorter than the rate of anthropogenic climate change" and that "the discovery that advantageous offspring phenotypes are produced within two generations could indicate that some tropical marine species are more capable of coping with global warming than has been suggested."